1. Field of the Invention:
This invention relates to a drop-down door construction, such as for use on a cooking oven or automatic dishwasher. The door is provided with a counterbalance spring system that is tailored to balance the weight of the door and assist in the opening and closing movements of the door.
2. Description of the Prior Art:
The present invention is particularly useful as the counterbalance system for the door of a built-in wall oven or a range construction that is not provided with a drawer space or other extension beneath the oven which would otherwise allow the use of a generally vertical counterbalance tension spring. If there is little space beneath the oven, then the counterbalance tension spring must be arranged in a generally horizontal position, and attached at one end to the oven cabinet near the rear thereof. There is a certain amount of adjustability available in the prior art door counterbalance systems in order to accommodate oven doors of different weights depending upon whether they are solid doors, that is without a window; or an oven door with a window; or a door with a full glass front panel with a small window, which is widely being used in the oven art at this time; or the door of a pyrolytic self-cleaning oven which is much thicker in order to accommodate an extra amount of thermal insulation and door gasket material for sealing the door during the high temperature self-cleaning cycle. In such cases, it is possible to attach the tension spring in a variety of different attachment slots in order to change the initial tension applied to the spring, as well as its angle of operation.
One example of a counterbalance spring mechanism for an oven door that employs a vertical tension spring is shown in the patent of Roy D. Chisholm and William J. Cleary U.S. Pat. No. 3,132,640, which is assigned to the same assignee as is the present invention. Another counterbalance spring patent showing a variety of modifications of either vertical or horizontal tension springs is shown on a dishwasher; namely, U.S. Pat. No. 3,453,779.
The principal object of the present invention is to provide a drop-down door construction with a counterbalance spring mechanism where the door balancing torque substantially equals the torque of the door as it moves between a vertical closed position and a horizontal fully open position.
A further object of the present invention is to provide a door counterbalancing system of the class described employing a generally horizontal tension spring in cooperation with a swing link such that the moment art of the door balancing torque increases during the latter portion of the door movement from the vertical closed position to a horizontal fully open position.
A further object of the present invention is to provide a counterbalance system of the class described without relying on a complete system of rollers acting upon cam surfaces on the hinge lever so as to minimize relative movement, friction, wear and noise between the parts.